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99 lines
3.4 KiB
99 lines
3.4 KiB
/*Find the minimum value which satisfies the linear inequality:
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a*x + b*y >= 1 {a,b,x,y Integers} {a,b > 0} {a,b entered on command line}
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Nigel_Galloway@operamail.com
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February 2008
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*/
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using System;
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using System.Runtime.InteropServices;
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unsafe class GLPK{
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double *lp;
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public int a;
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public int b;
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const string glpkLibrary = "libglpk.so";
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readonly int GLP_FR = 1;
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readonly int GLP_IV = 2;
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readonly int GLP_DB = 4;
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struct ConstraintMatrix{
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public fixed int ia[3];
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public fixed int ja[3];
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public fixed double ar[3];
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}
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[DllImport(glpkLibrary, SetLastError=true)]
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static extern double* glp_create_prob();
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[DllImport(glpkLibrary, SetLastError=true)]
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static extern void glp_add_rows(double* lp, int rows);
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[DllImport(glpkLibrary, SetLastError=true)]
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static extern void glp_add_cols(double* lp, int cols);
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[DllImport(glpkLibrary, SetLastError=true)]
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static extern void glp_set_col_bnds(double* lp, int col, int bound_type, double lower_bound, double upper_bound);
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[DllImport(glpkLibrary, SetLastError=true)]
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static extern void glp_set_col_kind(double* lp, int col, int kind);
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[DllImport(glpkLibrary, SetLastError=true)]
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static extern void glp_load_matrix(double* lp, int elements, int* ia, int* ja, double* ar);
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public GLPK(int a, int b){
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this.a = a;
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this.b = b;
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lp = glp_create_prob();
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//Col 1 is x, Col 2 is y
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glp_add_rows(lp, 1);
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glp_add_cols(lp, 2);
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glp_set_col_bnds(lp, 1, GLP_FR, 0.0, 0.0);
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glp_set_col_bnds(lp, 2, GLP_FR, 0.0, 0.0);
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glp_set_col_kind(lp, 1, GLP_IV);
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glp_set_col_kind(lp, 2, GLP_IV);
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//Row 1 is a*x + b*y
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ConstraintMatrix CM = new ConstraintMatrix();
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CM.ia[1]=1; CM.ja[1]=1; CM.ar[1]=a;
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CM.ia[2]=1; CM.ja[2]=2; CM.ar[2]=b;
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glp_load_matrix(lp, 2, CM.ia, CM.ja, CM.ar);
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Console.WriteLine("Hello Nigel");
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}
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[DllImport(glpkLibrary, SetLastError=true)]
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static extern void glp_set_row_bnds(double* lp, int row, int bound_type, double lower_bound, double upper_bound);
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[DllImport(glpkLibrary, SetLastError=true)]
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static extern void glp_simplex(double* lp, void* options);
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[DllImport(glpkLibrary, SetLastError=true)]
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static extern void glp_intopt(double* lp, void* options);
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[DllImport(glpkLibrary, SetLastError=true)]
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static extern double glp_mip_col_val(double* lp, int col);
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public int betterGuess(int upper_bound){
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//Find a new guess less than the old guess: 1 <= (a*x + b*y) <= (old guess - 1)
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glp_set_row_bnds(lp, 1, GLP_DB, 1.0, ((double)upper_bound)-0.5);
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glp_simplex(lp, null);
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glp_intopt(lp, null);
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int x = (int)glp_mip_col_val(lp, 1);
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int y = (int)glp_mip_col_val(lp, 2);
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int nextGuess = a*x + b*y;
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Console.WriteLine("x = {0}, y = {1}, a*x + b*y = {2}",x,y,nextGuess);
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return nextGuess;
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}
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[DllImport(glpkLibrary, SetLastError=true)]
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static extern void glp_delete_prob(double* lp);
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~GLPK(){
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glp_delete_prob(lp);
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Console.WriteLine("Goodbye Nigel");
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}
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}
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class test{
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static bool isMinimum(int a, int b, int guess){
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Console.WriteLine("Trying {0}",guess);
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if (a%guess > 0) return false;
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if (b%guess > 0) return false;
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Console.WriteLine("Solution is {0}",guess);
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return true;
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}
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public static void Main(string[] args){
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Console.WriteLine("a = {0}, b = {1}",args[0], args[1]);
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GLPK lp = new GLPK(Int32.Parse(args[0]),Int32.Parse(args[1]));
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int guess = (lp.a > lp.b) ? lp.b : lp.a;
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while (!isMinimum(lp.a,lp.b,guess)) guess = lp.betterGuess(guess);
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}
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}
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